Since the manufacturers began to support the motherboards of ATA-2 standard, the possibility of connection of two interface cables has appeared in the computer. One of these cables is called a primary one, and another cable is known as a secondary one. Two devices which referred to as master and slave can work on one cable. The cable is the line of general access for all devices connected to it. Accordingly, during each moment of time only one pair of devices - the controller and one of the stores - can carry out the exchange on a cable, but owing to technologies of access optimization the work of stores does not require exclusive possession of the bus that enables an efficient usage of the throughput of the bus, making an impression of independent and simultaneous work of the stores connected to one interface cable. However, if the total maximum speed of reading of two devices from a magnetic surface exceeds the throughput of the bus to which they are connected, it is recommended to place them on different channels. The store configuration as the master or slave device is provided with jumpers or switches on the device. The position of jumpers and switches is described in its case.
There is a variant of automatic assignment of the master device at which the device is independently configured as master or slave depending on a place on the interface cable. Some conditions should be fulfilled for this purpose:
- Both devices should be set to Cable Select mode (CSEL).
- Contact of 28 sockets from outside the controller of a motherboard should be earthed.
- On one of cable sockets, 28 contacts should be removed, or the wire of a cable connected to it is disconnected.
As a result, contact 28 on one socket of the cable appears to be earthed, and the store, having found it out, is automatically configured as the master device, while contact 28 on another socket seems to free, and the store is set as the slave device.
For an increase in throughput of the bus in ATA-4 standard, the 80-pin cable has been developed. This cable has 40 additional shielding earthed wires alternating through one between primary signal lines. Such decision reduces the mutual effect of separate signal conductors to each other, also reduces various hindrances and pickups on a cable that is necessary at work in Ultra DMA-3 mode and above. In 80-pin cable, there is no connection with a 34th conductor of a socket that allows the controller of a motherboard to distinguish it from 40-pin.